Flat electrical resistance heating element

Abstract

The invention is for a flat electrical heating resistance element, so called foil elements. Elements according to the invention can be used for many purposes, however, it is specially intended for use as heating elements for water beds. The object of the invention is to minimize the electromagnetic fields caused by the elements. The influence of such magnetic fields on humans is on the whole unknown why there is a common desire that the strength of these magnetic fields shall be as low as possible in order to minimize effects, if any. Heating elements according to the invention have electrical resistance wire or band placed in loops on a plastic foil surface, whereby the loops have four with each other parallel conductors, electrically connected so that in any given moment the direction of the current in the two outer conductors are in the same direction and in the two inner conductors in the same direction opposite to the outer conductors.

I claim: 
     
       1. A flat electrical heating element comprising: a supporting surface;   a pair of electrical conductors defining a single continuous loop on said supporting surface, said loop comprising four substantially parallel and spaced apart conductor lengths comprising two relatively adjacently disposed inner lengths and two outer lengths spaced apart by said inner lengths; and   means for connecting said conductors to a voltage source, said conductors are electrically connected so that the direction of current flow is the same in the outer two conductors and the direction of current flow in the inner two conductors is the same but opposite to the direction of current flow in the outer two conductors.   
     
     
       2. The heating element according to claim 1, wherein said conductors are two-by-two connected at one end thereof so that two pairs of parallel conductors are obtained. 
     
     
       3. The heating element according to claim 2, additionally comprising a terminal point at each conductor; means for connecting the terminal points of one pair of conductors to a voltage source; and   means for connecting the terminal points of the other pair of conductors to each other.   
     
     
       4. The heating element of claim 3, wherein the two connected terminal points of each pair of said conductors are not those of two adjacent conductors. 
     
     
       5. The heating element according to claim 1, wherein said loops are placed on said surface so that said conductors are parallel to each other, and the distance between said conductors is essentially the same between said four conductors and between respective conductors of adjacent loops.